Study on the effects of auxiliary condenser operation parameters on the performance of closed loop heat pump drying system

Abstract

Considering the problems of high energy consumption, complex system structure and low drying temperature in current industrial drying system of metal parts, a closed loop heat pump drying system with auxiliary condenser was designed and established. The effects of auxiliary condenser operation parameters on the circulating air temperature, coefficient of performance (COP), moisture extraction rate (MER) and specific moisture extraction rate (SMER) were experimentally investigated, where the compressor rotating speed, circulating air volume, cooling water inlet temperature and flow rate respectively were 3900 r•min−1, 539.8 m3•h−1, 5∼30 °C and 30.6∼50.1 kg•h−1. The results showed that the drying temperature gradually increased with increasing cooling water inlet temperature and decreasing cooling water flow rate. When the cooling water inlet temperature and flow rate respectively were 20 °C and 34.3 kg•h−1, the drying temperature was 70.02 °C, meeting the high temperature requirement of industrial drying. Besides, the cooling water flow rate had little influence on the system COP, while the system COP increased at first and then decreased with increasing cooling water inlet temperature, reaching its maximum value 5.64 when the cooling water inlet temperature was 20 °C. Moreover, when the cooling water inlet temperatures respectively were 20 °C and 5 °C with constant cooling water flow rate 34.3 kg•h−1, the system MER and SMER could reach their maximum values of 3.8 kg•h−1 and 1.68 kg•kW−1•h−1, showing excellent dehumidification capacity. These results can provide guidance for the popularization and application of heat pump drying technology in the industrial drying.